The invention relates to a fuel injection valve of an injection pump-line-nozzle system provided for a Diesel internal combustion engine with an injector holder and an injection valve needle which is disposed in an injector body so as to be longitudinally movable against a force applied thereto by a compression spring and which is surrounded by a pressure chamber to which fuel to be injected is supplied via a fuel supply passage.
DE 44 41 603 A1 discloses such a pump-line-nozzle system wherein fuel is supplied from a fuel injection pump by way of a fuel line to a fuel injector.
MTZ Motortechnische Zeitschrift 57(1996)4, FIG. 17, further shows a fuel injection valve wherein a spring-biased nozzle needle is longitudinally movably supported in an injector body wherein it is surrounded by a pressure chamber to which a fuel supply line leads. The nozzle needle is engaged via a pressure pin by a pressure bolt on which a compression spring acts. With this so-called two-spring nozzle holder combination, a stepped injection can be achieved since first only one spring but later both springs are activated. In this way, a noticeable noise reduction can be achieved.
It is the object of the present invention to provide a fuel injection valve with which, by appropriate control of the fuel return, the NOx emissions of the engine and also the generation of noises can be reduced.
In a fuel injection valve for a pump-line-injector system of an internal combustion engine comprising a fuel injector with a nozzle body, a nozzle needle longitudinally movably supported in the nozzle body between a seated nozzle closing position and a lift-off position assumed during fuel injection, the nozzle includes a fuel supply passage, a fuel drain passage, a connecting passage extending from the fuel supply passage to the fuel drain passage, and a spring-loaded pressure relief piston forming a control valve disposed in the path of the pressurized fuel from the fuel supply passage to the drain passage for controlling the pressure of the fuel supplied to the nozzle needle during fuel injection into a cylinder of the internal combustion engine.
With the pressure relief piston arranged in the return line so as to act as a control valve, a flow connection can be established during fuel injection between the fuel supply passage and the fuel return line returning fuel to the fuel tank for a short period whereby the fuel injection pressure can be lowered within a well-defined range of the pressure curve. As a result, the amount of fuel injected during that phase is reduced. In this way, the noise generation and the NOx emissions of the Diesel internal combustion engine as well as the fuel consumption can be positively influenced.
The invention will be described below in greater detail on the basis of the accompanying drawings.